The Anatomy, Embryology and Systematic Relationships of Eucommiaceae

Abstract

Abstract:

In this work examined were leaf and wood anatomy and embryogenesis under

LM and pollen morphology under SEM of Eucommia ulmoides Oliv. The results were used for

a comparison between the family and Ulmaceae and Hamamelidaceae respectively. The taxon-

omic rank and relationships of E. ulmoides were analyzed mainly based on the spiral thicken-

ings on lateral walls of vessels in the secondary xylem, the presence of iridoid, embryology and

palynology.

1. The present authors tend to support Keng's (1962) view that the spiral thickenings on la-

teral walls of vessels are the remnant of a primitive character. The spiral thickenings on lateral

walls of vessels in E. ulmoides (Plate 1: 9) are similar to those of some genera of the Hamameli-

daceae (e. g. Altingia Noronha), while vessels in Ulmaceae lack spiral thickenings on lateral

walls. The Eucommiaceae with simple perforations plates (Plate 1: 9) is more specialized than

the Hamamelidaceae.

2. Based on the fact that the Eucommiaceae contains iridoid compound and has unitegmic

ovules and cellular endosperm, Dahlgren (1980, 1983) places with uncertainty the family in Cor-

niflorae as an order, a treatment which is widely discrepant from those of Takhtajan (1980),

cronquist (1981) and thorne (1983). Though containing iridoid compound, the Eucommiaceae

is different from Corniflorae in a combination of characters in external morphology, woody

anatomy and embryology. The compound has also been found in Liquidambar L. (Hamameli-

daceae) but not in the Ulmaceae, which is another piece of evidence showing a close relation-

ship between Eucommiaceae and Hamamelidaceae.

3. The development of microsporangia and megasporangia, as observed in the present

work, is basically in accordance with that reported by Tang (1962) and Eckardt (1963), but

the haustoria present both at the micropylar end and at the chalazal end and 4-celled proembryo

of the Solanad Type are reported here for the first time.

It can be seen from Table 2 that the Eucommiaceae and the Hamamelidaceae have a nu-

mber of embryological characters in common For example, glandular tapetal cells in an-

thers are usually multinuclear; cytokinesis of meiosis of pollen mother cells is simultaneous;

microspores develop into tetrahedral; ovules are anatropous, crassinucellate; embryo sacs are

of the monosporic Polygonum Type; endosperm is cellular (Plate 3: 5-7; 4: 1-3; 5: 1-3;

Fig. 1: 1-3,5). The Eucommiaceae is also embryologically related to the family Ulmaceae,

but the family under study is more specialized than the two families mentioned above in uni-

tegminy (Plate 4: 3,4), proembryo of the Solanad Type (Plate 6: 3; Fig. 2: 4), coexistence

of micropylar haustoium (Plate 6: 4-6) and chalazal hustorium, especially in the Eucom-

miaceae the epidermis and the endothecium are widely separate (Plate 3:3), a feature which

has never been seen in angiosperms to our knowledge.

4. Pollen grains of the Eucommiaceae are tricolporate (Plate 1: 5, 6, 8) and similar to

tricolporate ones of Rhodoleia championii in the Hamamelidaceae, but distinctly different

from porate pollen grains of the Ulmaceae.

5. Based on the specialized embryological features of the Eucommiaceae pointed out ab-

ove, the present authors tend to support the separation of the Eucommiaceae at an independent

order-Eucommiales by Takhtajan (1980) and Cronquist (1981). Considering the spiral

thickenings of vessels on lateral walls and the presence of iridoid in the Eucommiaceae, and

the similarities and differences in embryology and palynology among Eucommiaceae, Ham-

amelidaceae and Ulmaceae, the authors suggest that the Eucommiaceae is more closely related

to the Hamamelidaceae than to the Ulmaceae, and postulate that the Ulmaceae (in Urticales)

and the Eucommiaceae (Eucommiales) diverged from an earlier ancestor.

Key words: Eucommiaceae, Ulmaceae, Hamamelidaceae, Wood, Embryology, Iridoid, Systematic position

Zhang Zhi-Yu, Lu An-Ming, Pan Kai-Yu, Wen Jie. The Anatomy, Embryology and Systematic Relationships of Eucommiaceae[J]. .

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The Anatomy, Embryology and Systematic Relationships of Eucommiaceae

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